1. Field of the Invention
This invention relates to methods and apparatus for coupling an electrical cable to an electrical submersible pump electric motor.
2. Description of the Related Art
A pothead describes in general a device that couples an electrical cable to an electrical submersible pump (ESP) electrical motor. There are many conventional methods to achieve such coupling. Such conventional methods require a seal to be made between the pothead and electrical cable by according to two primary methodologies.
In the first methodology, a pothead connection assembly or matching mold is assembled with uncured rubber, which is then baked in the assembly for a length of time so the rubber will cure. In this process, the rubber will fill all of the voids and will set. As there is no free space left within the pothead assembly, during operation at elevated temperatures, there will not be sufficient room for thermal expansion of the rubber. As such, the rubber may exert excessive stress on the cable insulation and pothead internal components, thus limiting the maximum operation temperature to approximately 375° F. depending upon the type of material used.
In the second methodology, an axial, compressive force is applied to an elastic/pliable material (rubber, plastics, polyimide etc.) by a pair of oppositely positioned insulators, which distributes the force radially, similar in function to a compression fitting. According to this methodology, a seal is preloaded in a fixed volumetric space. Thus, when the temperature around the seal increases, it has no relief from the thermal expansion—again limiting the maximum operation temperature.
In a third methodology, longitudinally extending springs have been employed to try to limit the amount of excessive compressive force being applied as a result of thermal expansion. According to such methodology, when the compressive force becomes excessive, the longitudinally extending springs are compressed to allow the oppositely positioned insulators to separate. Nevertheless, besides the added complexity, forces may still be applied radially to the cable insulation prior to the rubber expanding longitudinally.
Further, each of the above methodologies are still affected by swelling of the rubber due to exposure to a dielectric oil, e.g., mineral oil, from the motor and/or hydrocarbons from within the well.
Recognized, therefore, by the inventor is the need for a pothead connector, boot seal assembly, and boot seal which can provide a seal upon installation and at lower temperatures, that also accounts for both thermal expansion and expansion due to contamination with motor oil and production fluid.